1. Field of the Invention
This invention relates to a vibration-insulative support member for supporting a structure, such as a building structure and an apparatus, from below so as to prevent vibration, caused for example by an earthquake, from being transmitted to such a structure.
2. Prior Art
There are known various vibration-insulative support members for supporting a structure, such as a building structure and an apparatus, from below. One such example is a compression spring as disclosed in Japanese Laid-Open (Kokai) Patent Application No. 49051/74. This compression spring is formed by coating a plurality of cord fabrics, each composed of steel cords or the like arranged biaswise, with rubber, and winding the thus rubberized cord fabrics around a cylindrical body of rubber to form a plurality of layers, the directions of the cords of each adjacent layers of cord fabrics being opposite to each other.
Another example is a vibration-insulative device as disclosed in Japanese Laid-Open Patent Application No. 211471/87. This vibration-insulative device is formed by alternately laminating rigid plates, such as steel plates, and soft plates, such as rubber plates and bonding them together to form a laminate, forming a cylindrical hole a central portion of the laminate, and sealing a viscous material such as aromatic oil in the cylindrical hole.
The above-mentioned compression spring disclosed in Japanese Laid-Open Patent Application No. 49051/74 is adapted for use in an automobile suspension. Since the cylindrical body of rubber is covered by the rubberized cord fabrics having the cords arranged biaswise, such a compression spring has such a low longitudinal rigidity that it can efficiently absorb vertical vibration. On the other hand, the compression spring has such a high transverse rigidity that the layers between which such compression springs are interposed can not be easily displaced relative to each other in a horizontal direction. Therefore, when the ground is subjected to a horizontal quake, the structure supported thereon could not be brought into a stationary condition. For this reason, such compression spring could not be used as a vibration-isolation member.
Since the vibration-isolation device disclosed in Japanese Laid-Open Patent Application No. 211471/87 comprises the rigid and soft plates stacked alternately one upon another, the transverse rigidity can be lowered by reducing the thickness of each plate and increasing the number of the stacked plates, thereby enhancing a vibration-isoration effect. In such a case, however, since the thickness of the rubber layer is reduced, the longitudinal rigidity is increased, so that an vibration-insulative ability in the vertical direction is lowered, and in addition the use of such an increased number of the stacked plates has made the manufacture difficult.